Cycad description

With a fossil history that dates back over 150 million years ago, the cycads are the most primitive living seed plants (4)(5). Although not as attractive as some other cycads, Dioon caputoi is noted for its curiously narrow and widely spaced bluish-green leaflets (2)(6). With stems rarely growing above a metre in height, D. caputoi is a relatively small species. Like all cycads, the stems have a woody appearance, but are mostly comprised of soft, pithy storage tissue protected by a solid layer of old leaf bases (2)(7). The reproductive organs of cycads take the form of cones, similar in appearance to those of a conifer (8), with the male and female cones being borne on separate plants (2). Both sexes of D. caputoi only produce a single, pale brown cone on each stem, with the seed cone being shaped like an egg, while the pollen cone is slightly more elongate (2)(7).

Related species

Cycad biology

Cycads are long-lived, slow growing plants that always occur as individual male or female plants (2)(7). There is no way of determining the sex of a cycad until it begins to produce its first cone (2). For a long time cycads were thought, like cone-producing conifers, to be entirely wind pollinated (10). However, studies now suggest that the vast majority, if not all cycads, are actually pollinated by insects or more specifically weevils (2)(7)(10). To attract pollinators, male and female cones produce powerful odours, usually in the early morning or evening (2). Travelling between the sexes, the weevils pollinate the plants by inadvertently transferring pollen from the male cones to the receptive ovules of the female cones (2)(11).

The seeds produced by cycads are large and have a fleshy outer coat, but are relatively short-lived and vulnerable to desiccation. The fleshy outer layer is desirable to a range of animals such as birds, rodents and bats, depending on the species of cycad and region it occupies. However, with any luck the unpalatable seed is discarded some distance away from the parent plant in a hospitable environment in which to germinate(7).

Cycad status

Cycad threats

Deforestation for logging and agriculture has occurred throughout the new world, and this has had a dramatic effect on many cycad species, especially those that grow in the understorey of forests. Although collecting of plants from the wild in the new world has been less severe than in parts of Africa, several Mexican species, including D. caputoi, have been decimated by collectors (4). During the 1980s in particular, local people report that large numbers of D. caputoi were extracted illegally. None of the four remaining populations of D. caputoi number more than 120 individuals, and all are mostly comprised of adult plants due to poor natural recruitment of seedlings (5).

Cycad conservation

Dioon caputoi receives some protection from international trade under its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (3). Nonetheless, a range of additional conservation measures are still urgently needed for this Critically Endangered species. This includes: efforts to halt the illegal extraction of plants and further deforestation within the remaining populations; the monitoring of population dynamics as part of a long-term management plan; and the reintroduction of artificially propagated plants (5).

Authentication

Glossary

The beginning of growth, usually following a period of dormancy and in response to favourable conditions. For example, the sprouting of a seedling from a seed.

Ovules

A structure within the female reproductive organs of plants that contains eggs and when fertilized by pollen, develops into seeds.

Pollinate

To transfer pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.

Pollinators

Animals that in the act of visiting a plant's flowers transfer pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.

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